Device and method for using the device for &#34;in situ&#34; extraction of bitumen or ultraheavy oil from oil sand deposits

ABSTRACT

The device has at least one electrical conductor loop formed of a feed conductor, a return conductor and an inductor connected therebetween. At least the inductor is at least partially or completely disposed in the oil sand deposit. The device further has an alternating current generator that is electrically connected to the at least one conductor loop by at least two electrical contact points. The alternating current generator has a transformer with at least one primary and at least one secondary winding. The at least one secondary winding comprises a center tap to which a ground potential U e  is electrically connected.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International Application No. PCT/EP11/066651, filed Sep. 26, 2011 and claims the benefit thereof. The International Application claims the benefit of German Application No. 102010041434.4 filed on Sep. 27, 2010 and German Application No. 102010043529.5 filed on Nov. 8, 2010, all applications are incorporated by reference herein in their entirety.

BACKGROUND

Described below is a device and a method for using the device for the “in situ” extraction of bitumen or ultraheavy oil from oil sand deposits. The device includes at least one electrical conductor loop, which has a forward conductor and a return conductor and an inductor connected therebetween, wherein at least the inductor is arranged at least partially or completely in the oil sand deposit. Furthermore, the device includes an AC generator, which is electrically connected to the at least one conductor loop via at least two electrical contact points. The AC generator includes a transformer having at least one primary winding and at least one secondary winding.

Bitumen or ultraheavy oil can be removed from oil sand or oil shale deposits (merely referred to below as oil sand deposits or reservoirs for reasons of simplicity) in mining or by “in situ” extraction. “In situ” extraction includes the introduction of solvents or thinners and/or the heating of the ground of the oil sand deposits in order to make the ultraheavy oil or bitumen free-flowing or to be able to pump away the ultraheavy oil or bitumen. A much used procedure for “in situ” extraction is based on the SAGD (Steam Assisted Gravity Drainage) method. In this case, steam is introduced at elevated pressure into the ground through a pipe running horizontally within the reservoir. The heated, free-flowing ultraheavy oil or bitumen trickles to a second pipe, for example one which is approximately 5 m deeper, by which it is pumped away or conveyed.

DE 102007040605 B3 discloses a method in which the heating of the ground of an oil sand deposit takes place inductively via an electrical/electromagnetic heating method. With the method, heating of unconventional heavy oil with viscosities of, for example, 5° API to 15° API from temperatures of approximately 10° C. ambient temperature up to 280° C. is possible. As a result, the oil can flow in a gravitational process, owing to the improvement in the fluidity, to the lower impermeable boundary layer of the reservoir and from there can flow away by known drainage production pipes in order to either be pumped to the Earth's surface by lift pumps or to be conveyed to the surface, overcoming the force of gravity, by the pressure built up in the reservoir by heating and/or introduction of steam.

The electromagnetic heating process can in particular be combined with a steam process, which ensures improved permeability and/or conductivity. It is also possible for the steam stimulation by the production pipe to be allowed to take place cyclically at the beginning of the heating phase or later.

The electrical/electromagnetic heating method is implemented with the aid of at least one electrical conductor loop, which is supplied electrical power or AC current/voltage by an AC generator. As a result, “in situ” extraction below the surface to depths of up to several 100 meters is possible. The conductor loop in conjunction with the AC generator forms, in the state in which current is flowing, a resonant circuit, which produces an alternating magnetic field in the environment of the conductor loop in the reservoir, by which alternating magnetic field eddy currents are produced in the environment of the conductor loop. The eddy currents result in heating of the reservoir and therefore in liquefaction of the ultraheavy oil or bitumen.

In order to achieve a good heating power in the MW range, the conductor loop needs to be supplied an electrical voltage of up to 10 kV or even greater by the AC generator. This means that the electrical voltage of up to 10 kV or higher is present at connection terminals, which electrically connect the conductor loop to the AC generator, and that the voltage can drift freely towards the ground potential. In order to reliably prevent electrical flashovers or arcs from a connection of the conductor loop to the surrounding ground, a dielectric strength which is higher than the maximum clamping voltage by a factor X, which may be 2 to 10, for example, should be provided. This results in a high degree of complexity in terms of insulation and high costs.

SUMMARY

Described below are a device and a method for using the device for “in situ” extraction of bitumen or ultraheavy oil from oil sand deposits which reduce the insulation complexity and any costs associated therewith. In this case, reliable insulation of the terminals with respect to the environment should also be provided at high electrical heating powers.

A device for the “in situ” extraction of bitumen or ultraheavy oil from oil sand deposits has at least one electrical conductor loop, which has a forward conductor and a return conductor and an inductor connected therebetween. The inductor is arranged at least partially or completely in the oil sand deposit. The forward conductor and the return conductor can also act as inductor or produce the inductor identically, wherein the conductor loop in the latter case is formed from a continuous conductor. In the text which follows, for reasons of simplicity, a forward conductor and a return conductor and an inductor connected therebetween are described even when the forward conductor and the return conductor act as inductor or produce the inductor identically. A forward conductor and a return conductor and an inductor connected therebetween should thus correspondingly also be understood to mean a forward conductor and a return conductor which act as inductor or produce the inductor identically. Furthermore, the device includes an AC generator, which is electrically connected to the at least one conductor loop via at least two electrical contact points. The AC generator in this case includes a transformer having at least one primary winding and at least one secondary winding. The at least one secondary winding has a center tap, to which a ground potential UE has been applied electrically.

By virtue of the application of the ground potential UE or grounding of the center tap, the maximum electrical output voltage which is present across the conductor loop between the contact points is limited to half the maximum output voltage, for example. This results in a considerably lower requirement in terms of insulation for the contact points with respect to the ground in the environment for preventing flashovers or arcs effectively and reliably. The lower insulation requirement is also associated with lower costs. The voltage is thus effectively prevented from drifting freely at the contact points with respect to the environment or the ground.

The ground potential UE can have been applied passively electrically via a galvanic connection to the center tap, which results in a simple and inexpensive solution to the problem. Alternatively, the ground potential UE can have been applied actively to the center tap using circuitry via an electrical circuit. As a result, control or regulation using circuitry corresponding to the method requirements is possible.

As an alternative or in addition to the center tap at the at least one secondary winding, to which a ground potential UE has been applied electrically, a device for the “in situ” extraction of bitumen or ultraheavy oil from oil sand deposits having the above-described features has a ground potential UE, applied electrically at the conductor loop at a point spatially removed from the AC generator, with or without a center tap. The advantages are similar to the advantages associated with a ground potential UE at a center tap on the at least one secondary winding, as have been described previously.

The ground potential UE can have been applied spatially in a region on the conductor loop, in particular on the inductor, which is furthest removed from the AC generator. In general, the furthest removed point is in the region of halfway along the length of the conductor loop. Grounding at this point results in a maximum possible limitation of the maximum electrical output voltage which is present across the conductor loop between the contact points. The insulation requirement for the contact points can thus be reduced.

A voltage UH in the region of greater than 10 kV can have been applied via the inductor for inductively heating the oil sand deposit. This can result in a heating power in the MW range and is therefore sufficient for heating the ground such that bitumen or ultraheavy oil becomes free-flowing. The transformer can be in the form of a matching transformer for transforming an output voltage UA into a voltage in the region of the voltage UH.

The inductor can have a length of greater than 1 km, in particular of greater than 5 km. Thus, sufficient ground can be heated by the inductor in order to ensure usual oil extraction from oil sand deposits.

With the exception of a point on the AC generator and/or a point on the conductor loop spatially removed from the AC generator at which the ground potential UE can have been applied in each case, the electrical conductor loop can be electrically insulated completely from the oil sand deposit. In particular the ground potential UE can have been applied in such a way that heating of the oil sand deposit via the electrical conductor loop takes place purely inductively or at least substantially purely inductively. The at least one primary winding can be DC-isolated from the at least one secondary winding. The primary winding can be electrically connected to power converters. The AC generator can be in the form of an HF generator with an electrical power in the range of from 1 to several MW at 5 to 200 kHz, in particular 50 kHz. This arrangement and these values enable optimum heating of the oil sand deposit for extraction of bitumen or ultraheavy oil.

A method using the above-described device involves application of the ground potential UE at a point on the secondary winding and/or at a point on the conductor loop spatially removed from the AC generator, wherein the voltage between the contact points is reduced to a value which is lower than the value of an output voltage without the ground potential UE applied. The voltage between the contact points can be reduced to a value which is substantially half the value of an output voltage without the ground potential UE applied.

The advantages associated with the method for using a device as described above for the “in situ” extraction of bitumen or ultraheavy oil from oil sand deposits are similar to the advantages which were previously described in relation to the device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, but without any restrictions being imposed thereby, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a perspective view of an oil sand reservoir 1 with an electrical conductor loop 2 running in the reservoir 1, and

FIG. 2 is a circuit diagram of an embodiment of a device for the “in situ” extraction of bitumen or ultraheavy oil from oil sand deposits 1 corresponding to that shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 illustrates an oil sand deposit referred to as a reservoir, wherein a right-parallelepipedal unit 1 with the length l, the width w and the height h is always described for further considerations. The length l can be up to a few 500 m, the width w from 60 to 100 m and the height h approximately 20 to 100 m, for example. It is necessary to consider that, starting from the Earth's surface E, a “platform” with a thickness s of up to 500 m can be provided.

When implementing the SAGD method, an injection pipe for steam or water/steam mixture and a conveying pipe for the liquefied bitumen or oil are provided in the oil sand reservoir 1 of the deposit in a known manner, and in a manner which is not illustrated for reasons of simplicity, as is known from the related art, for example DE 102007040605 B3.

The arrangement or device illustrated in FIG. 1, which includes, inter alia, a conductor loop 2 which is arranged partially or completely in the reservoir 1, is provided for inductively heating the reservoir 1. This can take place in addition to or as an alternative to known heating with steam, for example. The conductor loop 2 laid in the ground, which conductor loop can have a length of from a few hundred meters up to several kilometers, for example, includes a forward conductor 10 and a return conductor 20 and an inductor 15. The forward conductor 10 and the return conductor 20 are routed next to one another, in particular into the ground and out of the ground, and the inductor 15 is connected electrically between the forward conductor and return conductor 10, 20. In general, the inductor 15 has a substantially U-shaped conductor, which is routed horizontally in the ground, wherein both parts of the U shape are routed at the same depth or lie one above the other.

The inductor 15 can be formed continuously from one conductor or be formed from two conductors, which are connected to one another at the U-shaped end via an element within or outside of the reservoir 1. Conductor in this context is always understood to mean electrical conductor below. The conductors 10 and 20 are routed vertically at the start or down into the ground at a flat angle. Typical distances between the forward conductor and the return conductor 10, 20 and/or between the two parts of the inductor 15 are 5 to 60 m given an outer diameter of the conductors of 10 to 50 cm. The conductors 10, 15 and 20 can also be formed from a continuous conductor or from conductor parts. Instead of a forward conductor and a return conductor 10, 20, the inductor 15 can also perform the task of the conductors or be routed into the ground corresponding to the profile of the conductors and replace the conductors.

An HF generator 30, which can be accommodated in an external housing, is electrically connected to the conductor loop 2 via connection terminals, for example, and supplies electrical power to the conductor loop. FIG. 1 does not show the connection terminals since they are located in the housing with the HF generator 30.

An electrical double line, as is known, for example, from DE 102007040605 B3, can be used as conductors 10, 20 and 15. A double line having the abovementioned typical dimensions has a longitudinal inductance per unit length of 1.0 to 2.7 μH/m. The transverse capacitance per unit length given the mentioned dimensions is only 10 to 100 μF/m, with the result that the capacitive quadrature currents can initially not be taken into consideration. In this case, wave effects should be avoided. A wave speed of an electrical wave is determined by the capacitance and inductance per unit length of the conductor arrangement.

The characteristic frequency of the arrangement is determined by the loop length and the wave propagation speed along the arrangement of the double line 10, 15, 20. The loop length should therefore be selected to be so short that no disruptive wave effects result here. The power loss density distribution in a plane perpendicular to the conductors, as is formed in the case of energization of the upper and lower conductors in phase opposition, decreases radially.

For an inductively introduced heating power of 1 kW per meter of double line, a current amplitude of approximately 350 A for low-resistance reservoirs with resistivities of 30 Ω·m and approximately 950 A for high-resistance reservoirs with resistivities of 500 Ω·m is required at 50 kHz. The required current amplitude for 1 kW/m is inversely proportional to the square of the excitation frequency, i.e. at 100 kHz, the current amplitudes decrease to ¼ of the above values. Given an average current amplitude of 500 A at 50 kHz and a typical inductance per unit length of 2 μH/m, the inductive voltage drop is approximately 300 V/m.

With the abovementioned total lengths of the double conductors 10, 15, 20, the total inductive voltage drop would add up to values of >100 kV. Such high voltages need to be avoided in order to reduce the risk of flashover in particular between the connection terminals and in order not to require large insulation layer thicknesses. The connection terminals need to be insulated from the reservoir 1 in respect of high voltages in order to suppress a resistive current flow. Thick insulation layers result in a high consumption of materials and high costs.

A solution to the problem can be provided by grounding a point on the conductor loop 2 in a region 15 or by grounding a center tap 70 of a secondary winding SE of a transformer 50 of the power generator 30. The latter is possible as a result of the circuit illustrated schematically in FIG. 2. The conductor loop 2 is formed by the forward and return conductors 10, 20 and the inductor 15. The forward and return conductors 10, 20 can also act as inductor 15 or the inductor identically, wherein the conductor loop 2 in the latter case is formed from a continuous conductor. The conductor loop 2 is connected electrically to a transformer 50 via connection terminals 40, 40′. The transformer 50 can match an output voltage UA to a voltage UH at a frequency which is optimum for the inductive heating with the conductor loop 2. As has already been described above, this is dependent on dimensions such as length, cross section or design of the lines or double lines 10, 15, 20 and frequency, for example.

The transformer 50 is formed from a primary coil PR and a secondary coil SE, for example. The primary coil PR is supplied electrical power from a current/voltage supply 60 with an output voltage UA. The output voltage UA is converted into a voltage UH for heating the inductor 15 by the transformer 50, wherein voltage losses on the forward and return lines 10, 20 have not been taken into consideration for reasons of simplicity. These voltage losses would, when added to the voltage UH, result in the voltage to be obtained or transformed at the secondary coil SE.

The device includes a center tap 70 on the secondary coil SE. A ground potential UE has been applied electrically to the center tap 70, i.e. the center tap is grounded. Without the center tap 70 and with complete insulation of the conductors 10, 20, 30, the total voltage UH would be present at the connection terminals 40, 40′, which voltage can be in the region of greater than 10 kV at the maximum in relation to the ground potential UE and would drift freely. As a result of a grounded center tap 70, the potential difference between the inductor 15 or the forward conductor 10 and return conductor 20 and the surrounding ground is safely limited to half the voltage UH between the connection terminals 40, 40′. Without fixing the potential at the center tap 70 or at the opposite end of the conductor loop 2, the potential of the conductor loop could drift freely and thus assume higher voltages at a branch on the forward conductor side or return conductor side than half the voltage UH with respect to the surrounding ground, which could result in flashovers or arcs. Depending on the arrangement of the center tap 70 on the secondary coil SE, voltage values differing from half the voltage can also be achieved at the connection terminals 40, 40′. This is dependent on the secondary coil SE being split into two parts by the center tap 70. A maximum possible reduction in the voltage present at the connection terminals 40, 40′ is, however, half the value of the voltage UH which is obtained when the secondary coil SE is split into two identical parts by the center tap 70.

An alternative possibility for reducing the maximum voltage present at the connection terminals 40, 40′ with respect to the surrounding environment is not illustrated in the figures for reasons of simplicity. Instead of or in addition to a center tap 70, as is illustrated in FIG. 2, the inductor 15 and/or the forward or return line 10, 20 can have a point at which a ground potential UE has been applied or which is grounded. This can take place by virtue of the insulation being interrupted at the point on a conductor 10, 15, 20 which is otherwise electrically insulated completely from the ground. A maximum reduction in the maximum voltage UH present at the connection terminals 40, 40′ takes place in a similar manner to in the exemplary embodiment of the center tap 70 when the ground potential or the voltage UE is applied at a point which is spatially removed from the connection terminals 40, 40′ to a maximum extent. In the case of an inductor 15 with a U shape, as is illustrated, for example, in FIG. 1, with two identical parts of the inductor being connected to one another by a U-shaped end, grounding of the point 15 with the U-shaped end results in the maximum reduction in the potential which is maximally present at the connection terminals 40, 40′. In general, grounding expediently takes place only at one of two possible points on the conductor loop 2, at the center tap 70 of the secondary winding or at the opposite point on the conductor loop 2 itself. If other points, such as, for example, points on the forward conductor 10 or return conductor 20, are brought or set to ground potential, the maximum possible reduction in the voltage between the inductor 15 and the ground to half the value of the maximum voltage UH present at the connection terminals 40, 40′ cannot be achieved.

Both in the exemplary embodiment illustrated in FIG. 2 with the grounded center tap 70 and in the last-described exemplary embodiment with a grounded point on the inductor 15 and/or the forward or return conductors 10, 20, grounding can take place passively or actively. Passively in this context means that grounding takes place via an electrical line or a direct electrical contact with the surrounding environment. Actively in this context means that grounding or application of the potential UE takes place via a regulated or controlled electrical circuit.

A description has been provided with particular reference to exemplary embodiments. Thus, combinations of the exemplary embodiments with one another and/or with exemplary embodiments from the related art are also possible, inter alia. It will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004). For example, it is possible for grounding at more than one point to be favorable, instead of grounding at one point, depending on the design and use of the device, in particular in the case of active grounding. Grounding of one of the two contact points 40, 40′ can also take place. As a result, although the full potential UH is present at the second contact point 40 or 40′, a reduction in the complexity in terms of insulation is possible owing to the fact that only the second contact point 40 or 40′ is insulated 

1-12. (canceled)
 13. A device for in situ extraction of bitumen or ultraheavy oil from oil sand deposits, comprising: at least one electrical conductor loop, each including a forward conductor, a return conductor and an inductor connected between the forward conductor and the return conductor, at least the inductor being arranged at least partially in the oil sound deposit; and an AC generator, electrically connected to the at least one conductor loop via at least two electrical contact points, the AC generator including a transformer having at least one primary winding and at least one secondary winding, the at least one secondary winding having a center tap to which a ground potential is applied electrically.
 14. The device as claimed in claim 13, wherein the ground potential is applied one of passively to the center tap electrically via a galvanic connection, and actively to the center tap using circuitry via an electrical circuit.
 15. A device for in situ extraction of bitumen or ultraheavy oil from oil sand deposits, comprising: at least one electrical conductor loop, each including a forward conductor, a return conductor and an inductor connected between the forward conductor and the return conductor, at least the inductor being arranged at least partially in the oil sound deposit; and an AC generator, electrically connected to the at least one conductor loop via at least two electrical contact points, the AC generator including a transformer having at least one primary winding and at least one secondary winding, the at least one secondary winding, a ground potential being applied electrically to the conductor loop at a point spatially removed from the AC generator.
 16. The device as claimed in claim 15, wherein the ground potential is applied spatially on the inductor at a furthest point on the conductor loop from the AC generator.
 17. The device as claimed in claim 16, wherein the AC generator applies a voltage of at least 10 kV via the inductor that inductively heats the oil sand deposit.
 18. The device as claimed in claim 17, wherein the transformer is a matching transformer the voltage of at least 10 kV.
 19. The device as claimed in claim 18, wherein the inductor has a length greater than 1 km
 20. The device as claimed in claim 19, wherein the inductor has a length greater than 5 km.
 21. The device as claimed in claim 19, wherein, except for where the ground potential has been applied, the electrical conductor loop is electrically insulated completely from the oil sand deposit, so that application of the ground potential results in heating of the oil sand deposit via the electrical conductor loop purely inductively.
 22. The device as claimed in claim 21, further comprising power converters electrically connected to the primary winding, and wherein the at least one primary winding is DC-isolated from the at least one secondary winding.
 23. The device as claimed in claim 22, wherein the AC generator is an HF generator with an electrical power of greater than 1 MW at 5 to 200 kHz
 24. The device as claimed in claim 23, wherein the AC generator is an HF generator with an electrical power of greater than 1 MW at substantially 50 kHz.
 25. A method for in situ extraction of bitumen or ultraheavy oil from oil sand deposits, comprising: installing a device with at least one electrical conductor loop, each including a forward conductor, a return conductor and an inductor connected between the forward conductor and the return conductor, at least the inductor being arranged at least partially in the oil sound deposit; and an AC generator, electrically connected to the at least one conductor loop via at least two electrical contact points, the AC generator including a transformer having at least one primary winding and at least one secondary winding, the at least one secondary winding having a center tap; and applying the ground potential at one of the center tap of the secondary winding and a point on the conductor loop spatially removed from the AC generator, so that a voltage between the at least two electrical contact points is lower than an output voltage without the ground potential applied.
 26. The method as claimed in claim 23, wherein said applying results in the voltage between the at least two electrical contact points being substantially half the output voltage without the ground potential applied. 